1. Field of the Invention
The present invention relates to a light irradiator and an image scanner using the light irradiator, and to an image forming apparatus using the image scanner.
2. Description of the Related Art
Some image scanners for use in image forming apparatuses such as photocopiers use light irradiators in which multiple light-emitting diodes (LED) (point light sources) are arranged in a straight line as light sources to irradiate documents with beams of light. Since illuminance ripple (variation of illuminance distribution) along the arrangement direction of the LEDs at the irradiation target (document) occurs, a light guiding member made of a transparent resin, glass, etc., is provided between the irradiation target and the point light sources.
This light guiding member guides the irradiation beams of light, which are emitted from the multiple point light sources and diffuse circularly, toward the surface of the document along the main scanning direction with regard to scanning the document to reduce the occurrence of illuminance ripple. This makes it possible to irradiate a wide target (document) with beams of light having a strong intensity even by using small LEDs as the light source.
JP-3187280-B1 (JP-H08-315621-A) and JP-3659770-B1 (JP-H10-322521-A) describe such structures. However, the structures described in JP-3187280-B1 (JP-H08-315621-A) and JP-3659770-B1 (JP-H10-322521-A) mentioned above have a problem in that irradiating a document along the main scanning direction evenly is difficult when the relative positions of the multiple LEDs and the light guiding member vary.
In a case in which a small light source having a relatively small light intensity such as LEDs is used, it is desired that the beams of light emitted from the light source enter the light guiding member as much as possible and from which the beams of light travel toward the target as much as possible while reducing the variation of the illuminance intensity. This demands a highly precise relative positioning of the light source and the light guiding member.
In an attempt to handle this demand, JP-4625279-B1 (JP-2006-025303-A) describes providing a positioning member for the LEDs (substrate) to maintain the relative positions of the light source and the light guiding member. However, although the precision of the relative positioning of the light source and the light guiding member is improved by providing the positioning member, the number of components necessarily increases, which is disadvantageous to manufacture a small and thin light irradiator.
In addition, if the positioning member is provided between the LED and the light guiding member, parts errors accumulate. This creates a concern about manufacturing in terms of more accurate assembly of the light source and the light guiding member. Furthermore, it is difficult to secure the relative positioning of the light source and the light guiding member if thermal conditions of the LED change.